1. Field of the Invention
The present invention relates to an ink, an ink cartridge, and an ink jet recording method.
2. Description of the Related Art
An ink jet recording method is a recording method involving applying a small ink droplet to a recording medium to form an image, and its popularization has been rapidly advancing in association with a reduction in its cost and an increase in recording speed. In general, a recorded product obtained by the ink jet recording method is inferior in image fastness compared with a silver halide photograph. In particular, when the recorded product is exposed to light, humidity, heat, or an environmental gas such as an ozone gas present in air for a long time period, the following problem arises. A coloring material of the recorded product deteriorates, and hence a change in color tone of its image or discoloration of the image is liable to occur.
Discoloration of an image recorded with an ink containing a black coloring material (black ink) often involves a change in its color tone due to the deterioration of the coloring material. In addition, the black ink is used in both of a monochromatic image and a full-color image, and in recent years, the ink has been required to be capable of recording an image having a high optical density not only when glossy paper is used but also when plain paper is used.
Polyazotization of a molecular structure of a black coloring material has been widely studied. For example, there are proposals concerning a trisazo compound having two naphthalene rings and a trisazo compound having a nitrogen-containing heterocycle (see Japanese Patent Application Laid-Open No. 2003-201412 and International Patent WO2007/077931A). In addition, there are proposals concerning a tetrakisazo compound having an electron-withdrawing group, a tetrakisazo compound having three naphthalene rings, and a tetrakisazo compound having a nitrogen-containing heterocycle (see International Patent WO2005/108502A, International Patent WO2005/097912A, International Patent WO2006/051850A, and Japanese Patent Application Laid-Open No. 2013-072061).